A. Field of the Invention
The invention relates to a process for cross-linking or degrading polymers, use being made of an organic peroxide which has at least one carbon-carbon double bond in the molecule. The invention also relates to shaped articles obtained by this process.
B. Description of the Related Art
A process of the above type is disclosed in U.S. Pat. No. 3,980,629. According to it the use as cross-linking agent of unsaturated peroxyketals leads to cross-linked polymers that are practically odourless and do not exhibit blooming.
Polymers having those properties are desirable in that, as is generally known, the more or less volatile decomposition products formed from dicumyl peroxide, which is often used in practice for cross-linking and degradation purposes, will lead to polymers which have an unpleasant smell and display blooming, which is objectionable to their applicability, for instance as packaging material for foodstuffs.
To the peroxyketals described in the above U.S. Patent, however, there is the disadvantage that the temperature at which they are incorporated into a polymer is subject to restrictions in view of the risk of premature decomposition. They are therefore not suitable at all to be used as a degradant for polymers such as polypropylene. When they are used as a cross-linking agent, this drawback manifests itself particularly in the cross-linking of those polymers, such as elastomers, into which the peroxide, and other additives, if desired, are to be mixed in at elevated temperature, prior to the polymer mass being shaped, to prevent premature cross-linking (scorching). The temperature at which these well-known peroxides are allowed to be processed is relatively low, which is detrimental to the viscosity and, hence, the processability of the polymer mass to be cross-linked. Therefore, as cross-linking agents these peroxyketals are no satisfactory alternative to dicumyl peroxide.